This invention relates to a cooling system for an electronic apparatus having heat-generating electronic components such as semiconductors, packaged in the apparatus, and more particularly to a cooling system which will be suitable for forced air cooling of such electronic apparatus.
In order to improve a packaging density, electronic apparatus having a large number of electronic components, such as semiconductor devices packaged therein, have generally included a construction wherein mother boards having a plurality of circuit boards to which the semiconductors and the like are attached, are stacked in a vertical direction and fitted to a rack or the like. In such an apparatus, the printed circuit boards of an upper stage mother board may not be cooled sufficiently if cooling wind is sent by only a blower disposed at the lowermost portion of the mounting rack.
In accordance with conventional cooling systems, a blower or blowers are often disposed at the upper portion, too, or each mother board is divided into a plurality of zones and a blower is disposed for each of these zones.
The problem with such conventional systems is that the cost of production will naturally increase with the increase of the number of blowers disposed and the packaging density will drop unavoidable.
Japanese Utility Model Laid-Open No. 162997/1980 proposes the arrangement wherein a heat diffusion plate made of a highly heat-conductive material on which a large number of air vent holes bored is interposed between the upper and lower mother boards. According to this prior art device, the heat of the cooling wind which is heated by the electronic components of a lower stage mother board is diffused by the thermal conduction effect of the heat diffusion plate while the wind passes therethrough and is radiated outside the mounting rack. Therefore, the prior art device can reduce the temperature rise of the cooling wind heated by the lower stage mother board and can send the cooling wind to the upper stage mother board.
In accordance with the prior art technique described above, there is a limit to the effect of making uniform the temperature distribution of the cooling wind while it passes through the diffusion plate. Namely, when the cooling wind from the blower is heated partially to certain extents by part of electronic components having a large exothermic quantity on the lower stage mother board, the cooling wind of this portion is sent to the upper stage mother board through the heat diffusion plate while keeping a higher temperature than the cooling wind of other portions. Therefore, the cooling effect on the electronic temperature is absorbed on the first device cooled, becomes lower than on the other portions of the upper stage mother board, and if the electronic components having a higher exothermic quantity are packaged together at this portion, then the temperature may even rise, contrary to the intended purpose of the system.
Current cooling technology needs require an improved cooling system that overcomes these problems and others, to provide a cooling system that has a minimal number of blowers, that increases the packaging density and which has the capability to send cooling wind to a post-stage by making a temperature distribution of the cooling wind substantially uniform.